Catalyst support

ABSTRACT

A catalyst support consisting mainly of synthetic silica, with 0.5-10 parts by weight of one or more oxides or phosphates of the elements of group IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA, IVA and the lanthanides characterised in that the support preparation method comprises mixing particulate synthetic silica with particulate oxides or phospates of the elements of Groups IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA, IVA and the lanthanides, or with precursors thereof, a forming step and calcination. The catalyst support is used together with phosphoric acid in the production of alcohols from olefins by hydration.

INTRODUCTION AND BACKGROUND

This present invention relates to catalyst supports and in particular,to catalysts supported on such catalyst supports, for use in processesfor the hydration of olefins, e.g. in the production of ethanol orisopropanol. The present invention also relates to processes for thehydration of olefins, which employ phosphoric acid supported on suchcatalyst supports to catalyse the hydration reaction.

Hydration catalysts undergo ageing during operation, which isdiscernible by a reduction in activity and/or selectivity. Deactivationis frequently due to a reduction in the specific surface area of thesupport brought about by elevated temperatures. Specific surface area inthe context of this application means the BET surface according towell-known method of Brunauer, Emmett and Teller determined by nitrogenadsorption according to DIN 66 132.

The specific surface area of support is closely related to its porestructure. Moreover, solids having a high surface area usually have acompletely or predominantly amorphous structure, which has a strongtendency to take on a thermodynamically stable state by crystallitegrowth accompanied by a reduction in specific surface area.

It has been found that catalyst supports containing silicon dioxide arealso subject to such ageing. Hydrothermal conditions accelerate ageing.Hydrothermal conditions prevail in chemical reactions in aqueous systemswhen the temperature is above the boiling point of water and pressure isabove standard pressure. It is furthermore known that contaminants, inparticular alkali metals, promote the ageing of supports containingsilicon dioxide under hydrothermal conditions (c.f. for example R. K.Iler in The chemistry of Silica, page 544, John Wiley & Sons (1979).

EP 0 578 441 B1 describes the use of a catalyst support for thehydration of olefins. The active component, which is brought onto thesupport by soaking, is phosphoric acid. This particular supportcomprises of pellets of synthetic silicon dioxide having high crushstrength, high porosity and few metallic contaminants. The purpose ofthe pores of the support is to accommodate the active component. Porevolume is thus preferably greater than 0.8 ml/g. Average pore radiusprior to use in the hydration process is in the range between 1 and 50nm.

In order to achieve optimum hydration performance, EP 0 578 441 B1specifies a silicon dioxide content of the support of at least 99 wt %with below 1 wt %, preferable below 0.3 wt % of contaminants. This typeof catalyst support has also been described in EP 0 393 356 B1 and inU.S. Pat. No. 5,086,031

It has surprisingly also been found that the catalyst supports based onsynthetic pyrogenically produced silicon dioxide described in EP 0 393356 B1 are also subject to ageing under hydrothermal conditions. Whereinsmall pores combine to yield larger pores with loss of specific surfacearea. Initially, pore volume remains virtually unchanged during suchageing. This ageing is unexpected because the pyrogenic silicon dioxideof which the supports consist has excellent temperature resistanceaccording to investigations with a scanning electron microscope, themorphology of pyrogenic silicon dioxide does not change on heating totemperatures of up to 1000° C. for a period of 7 days (SchriftenreihePigmente Nr. 11: Grundlage von Aerosil®; Degussa publication, 5thedition, June 1993, page 20).

Klimenko (U.S. Pat. No. 3,311,568) has described the positive influenceof TiO₂ on the lifetime of a phosphoric acid loaded, naturally occurringsiliceous support in the hydration of unsaturated hydrocarbons. At thattime it was believed that natural siliceous deposits such as diatomite,kieselguhr or diatomaceous earth were the most suitable supports forthese applications. However, naturally occurring siliceous materialsalways contain impurities that have some adverse effects on thecatalytic properties. These adverse affects can be diminished, as isdemonstrated in a number of patents, e.g. DE 37 09 401 A1, EP 0 018 022B1, DE 29 29 919, DE 29 08 491, DE 1 156 772. This, however, requires asubstantial number of additional steps in the support/catalystpreparation.

In order to obtain a sufficient physical strength, Klimenko had tocalcine at a temperature from 1050 to 1350° C.; the calcination timebeing between 5 and 24 hours.

Schluechter et al. (U.S. Pat. No. 5,208,195) recognise that H3PO4containing catalysts based on synthetic silica-gels supports are highlyactive and possess a sufficient initial mechanical strength. However, asthey state, these supports have the remaining disadvantage that theamorphous silica partially crystallises during prolonged use underconditions of the hydration reaction. This is associated with a sharpdecrease in the specific surface area and hence in catalytic activityand with a decrease in mechanical strength. Because of these drawbacks,they prefer to work with naturally based siliceous materials whichrequire a large number of preparation steps, e.g. treatment with acid inorder to decrease the alumina content, until they are fit to be used asa support for hydration purposes.

Schluechter et al. describe the use of titanium dioxide in order toincrease the compressive strength of catalysts spheres which are largelybased on an essentially montmorillonite-containing clay, hence, anatural occurring material. The titanium dioxide is admixed with theacid treated clay and finely divided silica gel, the TiO₂ content is 1.5to 2.5 parts by weight, the content of synthetically produced silica gelis from 20 to 40 parts by weight. The mixture is optionally shaped andcalcined.

It is also known from the prior art that silica which is modified byimpregnation with a soluble Group IVB-compound, shows improvedstability, see e.g. EP 0 792 859 A2. Titanium is one of the elements ofGroup IVB. The silica support is modified with the stabilising elementusing the impregnation process, preferably by pore volume impregnation.

Pore volume impregnation is performed by dissolving a soluble compoundof the stabilising element in a volume of solvent which is equal to thepore volume of the catalyst support and then distributing the solution,for example by spraying, over the support, which may be rotated in apill coater during spraying in order to ensure uniform impregnation.

Both aqueous and organic solvents or mixtures thereof may be used forimpregnation. In industrial practice, water is generally preferred assolvent. Selection of the suitable solvent, however, is dependent uponthe stabilising element compound to be used. An organic titaniumcompound, such as for example tetrabutoxytitanium (Ti(C₄H₉O)₄, may alsobe used instead of aqueous titanium (III) chloride. In this case,butanol is a suitable solvent.

EP 0 792 859 (A2) shows that the degree of stabilisation of pyrogenicsilica increases with increasing Ti-content. However, the addition oftitanium leads to a decrease in pore volume, and, hence, a loweractivity of the catalyst. Therefore, the need exists to keep theTi-content as low as possible.

As is shown in the examples of the above mentioned patent application,the impregnation with aqueous solutions of TiCl₃ yields materials withonly limited stabilisation. At a comparable Ti-loading, the use of aTi-alcoholate gave much better results. These are thus clearly preferredas source for Ti. Since Ti-alcoholates cannot be dissolved in water,organic solvents have to be used in order to impregnate the stabilisingelement. Appropriate and costly precautions must be taken to avoid anyexplosion hazard in the manufacturing of the support.

The modification of supports by means of impregnation with a stabilisingelement requires a substantial number of steps before the finishedstabilised support is obtained. First of all, the support must beshaped, for instance by extrusion or by tabletting, then dried andcalcined. Next, the stabilising element needs to be impregnated, thendried again. Finally, the treated supports are calcined at temperaturesof between 160 and 900° C.

There is a need therefore for a less expensive and less hazardoussupport preparation method which, at the same time, still gives therequired high degree of stabilisation and leads at the same time to ahighly active and selective catalyst.

SUMMARY OF THE INVENTION

An object of the present invention is accordingly to provide catalystsupports consisting mainly of synthetic silicon dioxide which, incombination with phosphoric acid, exhibit improved ageing resistancewhen used under hydrothermal conditions and which, at the same time,have excellent activity and selectivity for the hydration of olefins tothe corresponding alcohols.

A further object of the present invention are hydration catalysts whichare based on the improved supports according to the invention and whichhave excellent activity and selectivity for the hydration of olefins tothe corresponding alcohols.

The above and other objects of this invention are achieved by a catalystsupport consisting mainly of synthetic silica, with 0.5-10 parts byweight of one or more oxides or phosphates of the elements of group IIA,IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA, IVA and the lanthanidescharacterised in that the support-preparation method comprises mixingparticulate synthetic silica with particulate oxides or phospates of theelements of Groups IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA,IVA and the lanthanides, or with precursors thereof, a forming step andcalcination.

The above and other objects of this invention are also achieved by thesupported phosphoric acid catalysts wherein the catalyst support,consisting mainly of synthetic silica, is modified by 0.5 to 10 parts byweight titanium dioxide and/or zirconium dioxide based on the totalweight of the calcined support, and in which the silica and the titaniaand/or zirconium dioxide are mixed, preferably, prior to the formingstep.

Thus, according to one aspect, the present invention provides a catalystsupport consisting mainly of synthetic silica, with 0.5-10 parts byweight of particulate oxides or phospates of the elements of Groups IIA,IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA, IVA and the lanthanides,or with precursors thereof, preferred titania and/or zirconium dioxidecharacterised in-that the support preparation method comprises mixingparticulate synthetic silica with particulate oxides or phospates of theelements of Groups IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA,IVA and the lanthanides, or with precursors thereof, preferred titaniaand/or zirconium dioxide, a forming step and calcination.

In preferred embodiments of the invention, the catalyst supportscomprise silica, titania or zirconium dioxide.

By mixing particulate oxides or phospates of the elements of Groups IIA,IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA, IVA and the lanthanides,or precursors thereof, preferred titania and/or zirconium dioxide withsilica in this manner, the particulate oxides or phospates of theelements of Groups IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA,IVA and the lanthanides, or precursors thereof, preferred titania and/orzirconium dioxide form domains within the structural framework of thecalcined support, and is not just a surface coating. Thus, according toanother aspect of the present invention, there is provided a catalystsupport comprising a structural framework of synthetic silica, whichframework contains domains of particulate oxides or phospates of theelements of Groups IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA,IVA and the lanthanides, or of precursors thereof, preferred titaniaand/or zirconium dioxide, wherein the particulate oxides or phospates ofthe elements of Groups IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB,IIIA, IVA and the lanthanides, or precursors thereof, preferred titaniaand/or zirconium dioxide, in said domains form 0.5 to 10 parts by weightbased on the total weight of the support.

The resulting support has an improved stability against ageing and issubstantially easier to produce than any of the materials from the stateof the art. Furthermore, it shows excellent activity and selectivity inthe hydration of olefins to alcohols. Thus, according to a furtheraspect, the present invention provides a process for the hydration ofolefins, said process comprising reacting an olefin with water in thepresence of phosphoric acid supported on one of the catalyst supportsdescribed above.

Another object of the present invention is the preparation method forthese supports. Such a method comprises: mixing particulate silica, with0.5 to 10 parts by weight of particulate oxides or phospates of theelements of Groups IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA,IVA and the lanthanides, or with precursors thereof, preferred titaniaand/or zirconium dioxide, based on the total weight of the support priorto the forming step;

-   -   a forming step and    -   calcining the formed material between 400 and 1050° C.

The method of the present invention is not only much more simple andeasier to carry out than the existing manufacturing technologies, but atthe same time also gives materials with improved activity and stability,with excellent selectivities.

DETAILED DESCRIPTION OF INVENTION

It has now been found, surprisingly, that the stability of phosphoricacid catalysts based on synthetic silica can be increased verysubstantially when the synthetic particulate silica is physicallyadmixed with particulate oxides or phospates of the elements of GroupsIIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA, IVA and thelanthanides, or with precursors thereof, preferred particulate titaniaand/or zirconium dioxide prior to the forming step.

The silicon dioxide used in accordance with the present inventionconsists mainly of synthetic silica. Silica gels, precipitated silica's,both produced by wet chemical methods, are suitable synthetic materials.Synthetic silicon dioxide produced by flame hydrolysis, so-calledpyrogenic or fumed silicon dioxide, is preferably used.

Fumed or pyrogenic silica is offered by Degussa-Huels under thetradename AEROSIL®.

To prepare AEROSIL®, a volatile silicon compound is sprayed into anoxyhydrogen gas flame consisting of hydrogen and air. In most casescompounds like silicon tetrachloride or SiMeCl₃ are used. Thesesubstances hydrolyse under the effect of the water produced in theoxyhydrogen gas reaction to give silicon dioxide and hydrochloric acid.The silicon dioxide, after leaving the flame, is introduced into aso-called coagulation zone where the AEROSIL® primary particles andprimary aggregates are agglomerated. The product produced in this stageas a type of aerosol is separated from the gaseous accompanyingsubstances in cyclones and then post-treated with moist hot air. As aresult of this process, the residual hydrochloric acid content drops tobelow 0.025%. Since the AEROSIL® at the end of this process is producedwith a bulk density of only about 15 g/l, a vacuum compaction processfollows, by means of which compacted densities of about 50 g/l or abovemay be produced.

The particle sizes of the products obtained in this way may be varied byvarying the reaction conditions, such as for example the flametemperature, the proportion of hydrogen or oxygen, the amount of silicontetrachloride, the residence time in the flame or the length of thecoagulation zone.

The titanium dioxide used in accordance with the present invention canbe of any source, for instance precipitated or fumed titania. Fumed orpyrogenic titanium dioxide is also offered by Degussa-Huels and isproduced by flame hydrolysis of volatile Ti-compounds, like e.g. TiCl₄.The process to make pyrogenic or fumed TiO₂ is similar to the Aerosil®process described above.

The titanium dioxide can consist of any of its crystalline modification,e.g. anatase or rutile or it can be wholly or partly amorphous. Mixturesof these different phases are also possible.

The zirconium dioxide used in accordance with the present invention canbe of any source, for instance precipitated or fumed zirconium dioxide.

Zirconium dioxide which can be used according to this invention is forinstance described in Ullmann's Encyclopedia of Industrial Chemistry,5^(th) Edition, Vol. A28, 543-571 published by VCH-Verlagsgesellschaftand in PhD Thesis from Patrick D. L. Mercera, titled “Zirconia as asupport for catalysts” Universiteit Twente, the Netherlands (1991).

Instead of using particulate oxides or phospates of the elements ofGroups IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA, IVA and thelanthanides, preferred particulate titania and/or zirconium dioxide, itis also possible to use one or more of their precursors, that uponcalcination are transformed into the corresponding oxide form. Forinstance, particulate Zr(OH)₄ can be used instead of or in addition toparticulate zirconium dioxide.

For use as support for phosphoric acid hydration catalysts, the contentof the particulate oxides or phospates of the elements of Groups IIA,IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA, IVA and the lanthanides,or precursors thereof, preferred titanium dioxide and/or zirconiumdioxide in the finished support is from 0.5 to 10 wt.-%, preferably from1 to 9 wt.-%, most preferably from 2.6 to 8 wt.-%, based on the totalweight of the support. Too high concentrations lead to loss of activitycaused by a reduction in pore volume by formation of Ti- and/orZr-phosphates. Too low concentrations, on the other hand, lead to aninsufficient stabilisation of the catalyst and, hence, a too shortlifetime.

The content of synthetic silica in the calcined support can be at last80%. The support preferably consists of particles with dimensionsbetween 0.8 and 10 mm, most preferably from 1.5 to 8 mm. Too smallparticles lead to an unacceptable pressure drop over the catalyst bedwhereas too large particles result in diffusion limitation and, hence,lower activity of the catalyst. The surface area of the fresh unloadedsupport is mainly determined by the starting compounds silica and theparticulate oxides or phospates of the elements of Groups IIA, IIIB,IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA, IVA and the lanthanides, orprecursors thereof, preferred and titania and/or zirconium dioxide andcan be anywhere from 5 to 600 m²/g, preferably from 10 to 400 m²/g.

One of the most important properties of support materials to be used inhydration catalysts is their pore volume. A higher pore volume enables ahigher uptake of phosphoric acid and thus leads to a higher activity ofthe catalyst. The pore volume can be anywhere from 0.5 to 1.8 ml/g,preferably from 0.8 to 1.5 ml/g, most preferably from 0.9 to 1.5 ml/g.

The support can exist in form of tablets, extrudates, spheres or beads.For extrudates and tablets the standard form is cylindrical, but allother shapes known in the art, e.g. rings, wagon wheels, trilobes,stars, etc. can be used as well. The front and back end of such tabletscan either be flat or capped.

The bulk density of the support is determined mainly by the pore volume,the titania and/or zirconium dioxide content and by the form anddimensions of the individual support particles. The bulk density canthus vary within a broad range and can be anywhere from 300 to 800 g/l.

Forming can consist of any forming technique. The preferred formingmethods for supports to be used in a fixed bed hydration process aretabletting, compression or extrusion.

In the process of support preparation, particulate synthetic silica in apreferably finely divided form is admixed with particulate oxides orphospates of the elements of Groups IIA, IIIB, IVB, VB, VIB, VIIB, VIII,IB, IIB, IIIA, IVA and the lanthanides, or with precursors thereof,preferred titania and/or zirconium dioxide, also in a preferably finelydivided form, together with water and forming additives, like lubricantsand/or pore builders. Optionally, silica sol or naturally occurringsilica can be added, their maximum content is 10 parts by weight, basedon the weight of the calcined support. The mixture is then thoroughlymixed or kneaded. Optionally, the mixture can be dried partially orcompletely before the forming step, especially in the case oftabletting. The mixture is brought into its final form by the chosenforming technique, e.g. extrusion, tabletting or compression.

Finely divided in this respect means that the silica and the particulateoxides or phospates of the elements of Groups IIA, IIIB, IVB, VB, VIB,VIIB, VIII, IB, IIB, IIIA, IVA and the lanthanides, or precursorsthereof, preferred titania and/or zirconium dioxide, prior to the mixingor kneading step consist of agglomerates preferably in the range of upto 100 μm, more preferably up to 50 μm. Agglomerates that are in thisrange, should be so loosely bound that they, in the mixing or kneadingstep, are reduced in size to such an extent that the final supportcomprises small domains of particulate oxides or phospates of theelements of Groups IIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA,IVA and the lanthanides, or of precursors thereof, preferred titaniaand/or zirconium dioxide.

Because the forming procedure includes physically admixing particulatesilica and particulate oxides or phospates of the elements of GroupsIIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA, IVA and thelanthanides, or precursors thereof, preferred titania and/or zirconiumdioxide, the finished support contains domains of particulate oxides orphospates of the elements of Groups IIA, IIIB, IVB, VB, VIB, VIIB, VIII,IB, IIB, IIIA, IVA and the lanthanides, or of precursors thereof,preferred titania and/or zirconium dioxide. The size and thedistribution of these domains throughout the formed support areimportant with respect to the stability. After the mixing or kneadingprocedure in conjunction with the forming step, e.g. extrusion ortabletting, and calcination, 50% or more of the domains of particulateoxides or phospates of the elements of Groups IIA, IIIB, IVB, VB, VIB,VIIB, VIII, IB, IIB, IIIA, IVA and the lanthanides, or precursorsthereof, preferred titania and/or zirconium dioxide, in the calcinedsupport are smaller than 2 μm in size. Preferably, at least 50% of thedomains of particulate oxides or phospates of the elements of GroupsIIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA, IVA and thelanthanides, or precursors thereof, preferred titania and/or zirconiumdioxide is smaller than 1 μm and more preferably, at least 50% of thedomains of particulate oxides or phospates of the elements of GroupsIIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA, IVA and thelanthanides, or precursors thereof, preferred titania and/or zirconiumdioxide is in the range below 0.8 μm. Most preferably, at least 90% ofthe domains of particulate oxides or phospates of the elements of GroupsIIA, IIIB, IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA, IVA and thelanthanides, or precursors thereof, preferred titania and/or zirconiumdioxide is in the range below 0.8 μm.

Forming additives can be all aids known in the art, they may forinstance have a binding or a lubricating or a pore building function.Examples are cellulose and its derivatives, polyethylene glycol, wax,ammonia or ammonia releasing compounds, polyvinylalcohols, starch,sugars, etc.

The contents of the different substances in the mixture is to beadjusted such that the consistency of the mixture is suitable for thechosen forming technique. Optionally, the mixture can be dried partiallyor completely before the forming step.

After the forming step, the shaped bodies are optionally dried and thencalcined. Whereas drying is normally carried out at temperatures below200° C., calcination takes place preferably between 400 and 1050° C.,most preferably between 450 and 1000° C. High calcination temperaturesare no problem since the support materials according to this inventionhave surprisingly good thermal stability. The duration of thecalcination can be anywhere from 15 minutes to several hours, dependingon the type and size of kiln in which the calcination is carried out.The calcination is preferably carried out in air.

The catalyst supports as described herein are particularly advantageousfor hydrating olefins to produce lower alkanols. For the hydration ofolefins, phosphoric acid is introduced into the catalyst support as theactive component. To this end, once the stabilised support has beencalcined, it may be loaded with an aqueous solution of phosphoric acid.The phosphoric acid solution may contain 15 to 85 wt. % of phosphoricacid relative to the total weight of the solution, preferably from 30 to65 wt.-%. Optionally, the impregnated support is dried before use toform the dried catalyst system. In the dried form, the catalyst may havea concentration of phosphoric acid ranging from 5 to 55 wt.-%,preferably from 20 to 50 wt.-% based on the total weight of the driedcatalyst system.

The phosphoric acid loading procedure can consist of any appropriatetechnique, e.g. immersion in an excess phosphoric acid solution,soaking, spray impregnation, dry impregnation, etc. The amount ofsolution can be equal to, larger than or smaller than the pore volume ofthe amount of support. Loading can be carried out at any pressure. Inorder to facilitate the uptake of the rather viscous phosphoricsolution, the loading of the support might advantageously be carried outat subambient pressure.

The catalysts according to the invention have a very good stabilityagainst ageing under hydrothermal conditons, e.g. the conditions thatare encountered during olefin hydration. If catalysts according to theinvention are aged for approximately 40-45 hours at 350-370° C. in thepresence of 15-18 bar water vapour, their pore size distribution issuch, that the major part of the pore volume is associated with poreswith a diameter smaller than 5 μm.

Changes to the pore structure of catalyst supports containing silicondioxide under hydrothermal conditions are investigated below.Conventional unstabilised and stabilised supports are compared with thenew stabilised supports.

As discussed above, the present invention also provides a process forthe hydration of olefins, said process comprising reacting an olefinwith water in the presence of a catalyst comprising phosphoric acidsupported on a catalyst support, characterised in that said catalystsupport comprises a structural framework of synthetic silica, whichframe work contains domains of a particulate oxide or phosphate of atleast one element selected from the group consisting of Groups IIA,IIIB, IVB, VB, VIB, VIIB, VIIIB, IB, IIB, IIIA, IVA and the lanthanideseries of the Periodic Table; said oxide or phosphate forming 0.5 to 10parts by weight of the total weight of the support.

Preferably, the frame work of the catalyst support contains domains oftitania and/or zirconium dioxide.

The olefins to be hydrated are suitably ethylene or propylene. Whereethylene is employed, the alcohol produced is ethanol. Where propyleneis employed, isopropanol and n-propanol are produced. Etherscorresponding to the olefin may also be formed as by-products during thereaction. The hydration is preferably carried out in the vapour phase,ie both the olefin and water are in the vapour phase during thereaction.

The hydration reaction is typically carried out by placing the catalystimpregnated support in a reactor, sealing the reactor and then heatingthe supported catalyst to the reaction temperature. The supportedcatalyst is preferably heated to a temperature from 170 to 300° C.depending upon the end product desired. For instance, if the end productis ethanol from ethylene, the supported catalyst is suitably heated from225 to 280° C., preferably from 230-260° C., more preferably from235-245° C. On the other hand, if the end product is iso-propanol andn-propanol from propylene, the supported catalyst is suitably heatedfrom 180-225° C., preferably from 185-205° C.

When the supported catalyst bed has attained the desired temperature, acharge of the olefin and water in the vapour state may be passed throughthe reactor. The mole ratio of water to olefin passing through thereactor may be in the range of from 0.15 to 0.50, preferably from 0.25to 0.45, more preferably from 0.30-0.40. The space velocity of watervapour/olefin mixture passing through the reactor may be subject toslight variations depending upon whether the reactant olefin is ethyleneor propylene. For instance, in the case of ethylene, the space velocityof the mixture thereof with water vapour is suitably from 0.010 to0.100, preferably from 0.020 to 0.050 grams per minute per cm 3 of thesupported catalyst. In the case of a mixture of propylene and watervapour, the space velocity is suitably in the from 0.010-0.100,preferably from 0.02-0.07 g/min/cm3 of the supported catalyst.

The hydration reaction may be carried out a pressure ranging from 2000to 24000 KPa. Within this range the hydration of ethylene is suitablycarried out at a pressure from 3000 to 10000 KPa, whereas the hydrationof propylene is suitably carried out at a pressure from 2000-7600 KPa.These and other aspects of the present invention will now be described,by way of illustration, with reference to the following Examples andaccompanying Figures.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plot of differential intrusion vs. Pore diameter for a porestructure of an unstabilised catalyst support after a hydrothermalageing test (comp. example 1);

FIG. 2 is a plot of differential intrusion vs. Pore diameter for a porestructure of a catalyst support stabilised with 1.5% of titanium,according to prior art, after a hydrothermal ageing test (comp. example2);

FIG. 3 is a plot of differential intrusion vs. Pore diameter for a porestructure of a catalyst support stabilised with 4% of titanium,according to prior art, after a hydrothermal ageing test (comp. example3);

FIG. 4 is a plot of differential intrusion vs. pore diameter for a porestructure of a catalyst support stabilised with 5% of titanium,according to prior art, after a hydrothermal ageing test (comp. example4);

FIG. 5 is a plot of differential intrusion vs. pore diameter for a porestructure of a catalyst support stabilised with 5% of titanium,according to prior art, after a hydrothermal ageing test (comp. example5);

FIG. 6 is a plot of differential intrusion vs. pore diameter for a porestructure of a catalyst support stabilised with 3% of titanium,according to this invention, after a hydrothermal ageing test (example6);

FIG. 7 is a plot of differential intrusion vs. pore diameter for a porestructure of a catalyst support stabilised with 1.8% of titanium,according to this invention, after a hydrothermal ageing test (example7);

FIG. 8 is a plot of differential intrusion vs. pore diameter for a porestructure of a catalyst support stabilised with 1.8% of titanium,according to this invention, after a hydrothermal ageing test (example8); and

FIG. 9 is a graph showing how the ethanol space time yield (STY) of anolefin hydration process varies with time, depending on the catalystemployed (Example 17).

FIG. 10 is a plot of differential intrusion vs. pore diameter for a porestructure of a catalyst support stabilised with 5% of zirconia,according to this invention, after a hydrothermal ageing test (example22).

The pore size distribution curves shown in FIGS. 1 to 8 and 10 weredetermined using the well-known Hg porosimetry method. They show thedifferential penetration (intrusion) of the mercury as a function ofpore diameter. Arbitrary units were selected for differential intrusionand the curves were each expanded over the available area of thediagram.

COMPARATIVE EXAMPLE 1

A state-of-the-art support was prepared according to example 2 of EP 393356 B1.

This support is thus made by mixing pyrogenic silica (AEROSIL®200 fromDegussa-Huels), magnesiumstearate, methylcellulose and urea, andsubsequent drying and tabletting. The calcination procedure consists oftwo steps: a first calcination at 250° C., and the final calcination at750° C. This product is sold by Degussa-Huels under either of the namesDegussa 350, Träger 350, Support 350 or Aerolysth 350 and has thefollowing properties: specific surface area approx. 180 m²/g; bulkdensity approx. 490 g/l; total pore volume approx. 0.8 cm³/g. Itconsists of tablets with a diameter of 6 mm, and a height of 5.5 mm.

This support material was loaded with a 60 wt.-% phosphoric acidsolution and heated to 350° C. in a high pressure apparatus at a steampressure of 15 bar for 41 hours.

The pore size distribution of the aged catalyst was determined by Hgporosimetry. The measured pore size distribution is shown graphically inFIG. 1.

The hydrothermally aged supports have a maximum in the pore sizedistribution at pore diameters of between 20 and 30 μm.

COMPARATIVE EXAMPLE 2

The catalyst support from comparative example 1 was modified with 1.5wt. % of Ti. In order to modify 100 g of support with 1.5 wt. % of Ti,33 g of a 15% titanium(III)chloride solution (TiCl₃) were diluted withwater to 80 ml, corresponding to the pore volume of the supportmaterial. The support material was impregnated with this solution.

After 30 minutes exposure to the solution, the support was dried in adrying cabinet at 100° C. for 3 hours and then calcined in a furnace at600° C. for a period of 4 hours. The support was then loaded with a 60wt.-% phosphoric acid solution and left in a high pressure apparatus ata steam pressure of 15 bar at 350° C. for 40 hours. The pore sizedistribution of the aged catalyst was again determined by Hgporosimetry. The pore size distribution is shown graphically in FIG. 2.

The maximum of the pore size distribution is between 10 and 20 μm. Incomparison with the undoped catalyst used in comparative Example 1, thecatalyst doped with 1.5 wt. % of Ti has a higher proportion of smallpores of a diameter of below 10 μm after ageing.

COMPARATIVE EXAMPLE 3

The catalyst support as described in comparative example 1 was modifiedwith 4 wt. % of Ti. In order to modify 100 g of support with 4 wt. % ofTi, 85.93 g of a 15% titanium(III)chloride solution were diluted withwater to 80 ml and distributed over the support to impregnate it.

After 30 minutes exposure to the solution, the support was dried in adrying cabinet at 100° C. for 3 hours and then calcined in a furnace at600° C. for a period of 4 hours. The support was then loaded with a 60wt.-% phosphoric acid solution and left in a high pressure apparatus ata steam pressure of 15 bar at 350° C. for 43 hours. The pore size,distribution of this specimen is very wide. The maximum of the pore sizedistribution is approximately 2 μm. In comparison with the undopedcatalyst used in Comparative Example 1, the catalyst doped with 4 wt. %of Ti has a high proportion of pores of a diameter of less than 10 μm.In comparison with the undoped catalyst from Comparative Example 1, thecatalyst doped with 4 wt. % of Ti is distinctly more stable and theenlargement of pore diameter is distinctly less marked.

COMPARATIVE EXAMPLE 4

The catalyst support as described in Comparative Example 1 was modifiedwith 5 wt. % of Ti. In order to modify 100 g of support with 5 wt. % oftitanium, 35.5 g of tetrabutoxytitanium (Ti(C₄H₉O)₄) were diluted to 80ml with butanol and distributed over the support. Specialexplosion-proof equipment was used during impregnation and drying inorder to avoid any risk of explosion.

After 30 minutes exposure to the solution, the support was dried in adrying cabinet at 100° C. for 3 hours and then calcined in a furnace at600° C. for a period of 4 hours.

The support was then loaded with phosphoric acid and heated to 350° C.in a high pressure apparatus at a steam pressure of 15 bar for 41.5hours. The pore size distribution of the aged catalyst was determined byHg porosimetry. The pore size distribution is shown graphically in FIG.4.

The maximum of the pore size distribution is approximately 0.7 μm. Thereare virtually no pores with a diameter greater than 3 μm. In comparisonwith the undoped catalyst from Comparative Example 1, the catalyst dopedwith 5 wt. % of Ti is distinctly more stable. The average pore diameterfor the catalyst doped with 5 wt. % of Ti is smaller by a factor of 35than in the case of the undoped catalyst from Comparative Example 1.

The preparation method in this example is based on the use of an organicsolvent. Industrial production of this Ti-containing support materialrequires the use of special explosion-proof equipment and buildings.Furthermore, large amounts of organic solvents have to be handled, andorganic wastes have to be burned or otherwise recycled. This material isthus difficult to produce and, hence, expensive.

COMPARATIVE EXAMPLE 5

A similarly prepared catalyst support as described in ComparativeExample 1 with a higher pore volume of 1.0 ml/g was modified with 5 wt.% of Ti by impregnation with titanylsulfate (TiOSO₄) which was dissolvedin water that contained some H₂O₂. This solution was distributed overthe support.

After 30 minutes exposure to the solution, the support was dried in adrying cabinet at 100° C. for 3 hours and then calcined in a furnace at600° C. for a period of 4 hours.

The support was then loaded with phosphoric acid and heated to 350° C.in a high pressure apparatus at a steam pressure of 15 bar for 45 hours.The pore size distribution of the aged catalyst was determined by Hgporosimetry. The pore size distribution is shown graphically in FIG. 5.

In comparison with the undoped catalyst from Comparative Example 1, thecatalyst doped with 5 wt. % of Ti is distinctly more stable.

EXAMPLE 6

A catalyst support in accordance with this invention was prepared bymixing 1.0 kg of pyrogenic silica (Aerosil® 200 V from Degussa-Huels,amorphous), 52.5 g of pyrogenic titania (P25 from Degussa-Huels,consisting of approx. 70-80% anatase and 20-30% of rutile, surface area50 m²/g, d₅₀ 3-4 μm), 21 g of methylcellulose, 50 g of wax, 5 g ofpolysaccharide, 10 g of a 30% ammonia solution and 1.9 kg of water. Themixture was kneaded for approx. 30 minutes and was subsequentlyextruded. After drying at 110° C., the material was calcined in air at750° C. for 3 hours. The obtained extrudates contain 5 wt.-% of TiO₂ and95% of SiO₂. 5% TiO₂ corresponds to a Ti-content of 3 wt.-%. Thediameter of the extrudates is 4.0 mm, the surface area is 175 m²/g, thepore volume is 0.99 ml/g, the bulk density 450 g/l and the crushstrength 47 N.

The support of this example was analysed with transmission electronmicroscopy (TEM). The titania domains are clearly visible in theamorphous silica matrix. The titania domains have a maximum size ofapproximately 0.3 μm.

The support of this example was also analysed with XRD. No peaks ofcrystalline silica were found. Titania peaks were present for bothanatase and rutile.

This support was loaded with phosphoric acid and heated to 370° C. in ahigh pressure apparatus at a steam pressure of 15 bar for approx. 45hours. The pore size distribution of the aged catalyst was determined byHg porosimetry. The pore size distribution is shown graphically in FIG.6. There are virtually no pores of a diameter greater than 3 μm,although the Ti-content is only 3 wt.-%.

EXAMPLE 7

Another catalyst support in accordance with this invention was preparedby mixing 970 g of pyrogenic silica, 30 g of pyrogenic titania, 21 g ofmethylcellulose, 50 g of wax, 5 g of polysaccharide, 10 g of a 30%ammonia solution and 1.9 kg of water. The mixture was kneaded forapprox. 30 minutes and was subsequently extruded. After drying at 110°C., the material was calcined in air at 850° C. for 3 hours. Theobtained extrudates contain 3% of TiO₂ and 97% of SiO₂. 3% TiO₂corresponds to a Ti-content of only 1.8 wt.-%. The diameter of theextrudates is 3.5 mm, the surface, area is 165 m²/g, the pore volume is1.0 ml/g, the bulk density 440 g/l and the crush strength 50 N.

This support was loaded with phosphoric acid and heated to 370° C. in ahigh pressure apparatus at a steam pressure of 15 bar for approx. 43 hhours. The pore size distribution of the aged catalyst was determined byHg porosimetry. The pore size distribution is shown graphically in FIG.7. There are virtually no pores of a diameter greater than 3 μm. Incomparative example 2, the Ti-loading is 1.5 wt.-%, thus nearlyidentical to the Ti content of the support in this example. Comparisonof the porosimetry data shows that the support of the present inventionis much better stabilised. Furthermore, the support of the presentinvention is much easier to produce.

EXAMPLE 8

Another catalyst support in accordance with this invention was preparedby mixing 970 g of pyrogenic silica, 30 g of precipitated titania(anatase form), 21 g of methylcellulose, 50 g of wax, 5 g ofpolysaccharide, 10 g of a 30% ammonia solution and 1.9 kg of water. Themixture was kneaded for approx. 30 minutes and was subsequentlyextruded. After drying at 110° C., the material was calcined in air at850° C. for 3 hours. The obtained extrudates contain 3 wt.-% of TiO₂ and97 wt.-% of SiO₂. 3 wt.-% TiO₂ corresponds to a Ti-content of only 1.8wt.-%. The diameter of the extrudates is 3.5 mm, the surface area is 165m²/g, the pore volume is 1.0 ml/g, the bulk density 440 g/l and thecrush strength 50 N.

This support was loaded with phosphoric acid and heated to 370° C. in ahigh pressure apparatus at a steam pressure of 15 bar for 43.hours. Thepore size distribution of the aged catalyst was determined by Hgporosimetry. The pore size distribution is shown graphically in FIG. 8.There are virtually no pores of a diameter greater than 3.5 μm. Incomparative example 2, the Ti-loading is 1.5 wt.-%, thus nearlyidentical to the Ti content of the support in this example. Comparisonof the porosimetry data shows that the support of the present inventionis much better stabilised. Furthermore, the support of the presentinvention is much easier to produce.

EXAMPLE 9

The most frequently applied acid loading procedure consists of soakingthe support in an excess of approx. 60 wt.-% phosphoric acid solution.After this soak procedure, the excess solution is drained off and thecatalyst is dried.

During the soaking operation some of the titania present in the supportmight be dissolved. The loading procedure thus can lead to an unwantedloss of titania.

In some of the examples described above, the drained-off acid wasanalysed for the presence of titanium. Analysis was carried outsemi-quantitatively by adding some H₂O₂ to the acid solution. In thepresence of small amounts of titanium the solution turns yellow, highertitanium concentrations give an orange or red colour. Example Colourobserved 1 (comparative), without Ti none 3 (comparative) yellow 4(comparative) orange-red 5 (comparative) orange 6 very slightly yellow 7very slightly yellow

As can be seen from these results, the stabilised state-of-the-artsupports (examples 3, 4 and 5) suffer from substantial Ti-loss duringthe acid loading. The supports according to the invention do not loseany or only very little Ti. This is an advantage from the supportsaccording to the invention.

Other advantages have been demonstrated in the previous examples:compared to the state of the art supports, they have a better or equalhydrothermal stability after loading with phosphoric acid, their methodof preparation is much simpler and their titania content is lower.

EXAMPLE 10

A catalyst support according to the present invention was provided inthe form of 3.5 mm cylindrical extrudates. The method employed toprepare the catalyst support of this

Example is identical to that employed to prepare the catalyst support ofExample 6. The Ti content of the support was 3.9% wt/wt, as measured byX-ray Fluorescence. The support had a bulk density of 480 g/l, a porevolume of 0.96 ml/g (by H₂O absorption), a crush strength of 45N(average of 50 crushed pellets, using Mecmesin crush strength tester),and a pore size distribution characterised by a sharp unimodal peak at16 nm, as measured by Hg porosimetry.

EXAMPLE 11

A catalyst was produced by impregnating 1 litre of the support ofExample 10 with phosphoric acid. This was achieved by evacuating thepores of the support to approximately 35 mmHg, and then submerging theevacuated support in a 55.3 wt/wt % solution of orthophosphoric acid(H3PO4) The support was then left to soak in the solution at atmosphericpressure for 1 hour.

After soaking, the support was filtered free of excess acid, and driedat 120° C. for 24 hours. The bulk density of the resulting catalyst wasfound to be 874 g/l. The acid loading of the catalyst, as calculated bysubtraction of the support's bulk density, was 394 g/l.

The crush strength of the resulting catalyst was measured to be 49N(average of 50 crushed pellets, using Mecmesin crush strength tester).

EXAMPLE 12

The catalyst of Example 11 was used to catalyse an ethylene hydrationreaction.

The hydration reaction was carried out in a 1 litre continuous flowpilot plant, designed to simulate the reaction section of a gas phaseethylene hydration plant. The plant was operated as follows:

Fresh ethylene gas was fed to the plant from a high pressure ethylenecompressor. Liquid water was fed to the plant by diaphragm meteringpump. The feeds were combined with recycled ethylene and passed througha preheater/vaporiser, before being introduced to the catalyst bed.

The catalyst was held in a copper lined tubular reactor, which was alsofitted with a central multipoint thermocouple for accurately measuringcatalyst temperatures at various (fixed) depths down the catalyst bed.The gaseous reactor effluent was cooled to ambient temperature using asimple shell and tube type heat exchanger, and the mixture of liquid andgaseous products were separated in a high pressure gas/liquid separator.

The gaseous product, still containing significant levels of ethanol, wasthen further processed in a wash tower, where the majority of the watersoluble components was scrubbed out. The liquid effluent from the washtower was then mixed with the liquid effluent from the gas/liquidseparator to form the main product stream. This stream was collected andanalysed (by gas chromatography).

The scrubbed gas from the wash tower was fed to a recycle compressor andreturned to the reactor. The recycle gas flow rate was carefullycontrolled using a Coriolis meter to ensure that the contact timethrough the catalyst bed was similar to that employed in commercialethanol plants. An on-line gas chromatograph was also employed toanalyse the recycle stream every 15 minutes in order to determine therecycle gas composition.

The plant was operated at a pressure of 1000 psig (68 atm); a reactorinlet temperature of 240° C., a reactor exit temperature of 260° C.; a[water]:[ethylene] feed mole ratio of 0.35-0.36; a ethyleneGHSV=1350hr(−1); and a steam GHSV=485 hr (−1).

The catalyst was kept on stream for 2 weeks, during which time, thespace time yields (STYs) of ethanol, ether and acetaldehyde weremeasured. The results are shown in Table I below.

COMPARATIVE EXAMPLE 13

A catalyst was prepared by impregnating a Degussa 350 support withphosphoric acid using an analogous method as that described in Example11. The Degussa 350 support has been described in detail in comparativeexample 1.

The resulting catalyst was used to catalyse an ethylene hydrationreaction, using the 1 litre continuous flow pilot plant described inExample 12 above.

Table I below compares the space time yields (STY) obtained using acatalyst supported on the support of Example 10, with the STYs obtainedusing the phosphoric acid catalyst supported on Degussa 350 (ComparativeExample 13). TABLE I % ETHANOL ETHER ACETALDEHYDE SELEC- STY STY STYTIVITY SUPPORT (g/Lcat/hr) (g/Lcat/hr) (g/Lcat/hr) TO EtOH Comparative120 6.35 0.37 93.6 Example 13 Example 10 136 6.5  0.45 94.1

The results show that the catalyst supported on support of Example 10(i.e. the catalyst of Example 11) is more active and selective towardsethanol than a catalyst supported on Degussa 350 (Comparative Example13).

EXAMPLE 14

In this Example, the pore size distribution (PSD) of the catalyst ofExample 11 was measured before and after use. The fresh catalyst wasfound to have a pore size distribution characterised by a sharp unimodalpeak at 16 nm, as measured by Hg porosimetry. After use in the pilotplant as described in Example 12 above, the catalyst was found to bebi-modal at 165 and 380nm.

COMPARATIVE EXAMPLE 15

Example 14 above was repeated with a catalyst supported on Degussa 350.The Degussa 350 support has been described in detail in comparativeexample 1. The fresh catalyst was found to have a pore size distributioncharacterised by a sharp unimodal peak at 17 nm, as measured by Hgporosimetry. After use, the PSD of the catalyst was found to be bimodal,with peaks at 200 nm and 3000 nm. By comparing the results of Example 14and Comparative Example 15, it can be seen that the PSD of the catalystof the present invention changes significantly less than the PSD ofcatalysts supported on titania-free supports, such as Degussa 350.

EXAMPLE 16

A catalyst support according to the present invention was provided inthe form of 4 mm cylindrical extrudates. The method employed to preparethe support of this Example is identical to that employed to prepare thesupport of Example 6. The Ti content of the support was 4% wt/wt, asmeasured by X-ray Fluorescence. The support had a bulk density of 457.3g/l, a pore volume of 1.01 ml/g (by Hg porosimetry and H₂O absorption),a crush strength of 44.8N (average of 50 crushed pellets, using Mecmesincrush strength tester), and a pore size distribution characterised by asharp unimodal peak at 14.8 nm, as measured by Hg porosimetry.

EXAMPLE 17

A catalyst was produced by impregnating 8 litres of the support ofExample 16 with phosphoric acid. This was achieved by evacuating thepores of the support to less than 40 mmHg, and then submerging theevacuated support in a 52 wt/wt % solution of orthophosphoric acid(H3PO4) .The support was then left to soak in the solution atatmospheric pressure for 2 hours.

After soaking, the support was filtered free of excess acid, and driedat 120° C. for 3 days. The bulk density of the resulting catalyst wasfound to be 755.5 g/l. The acid loading of the catalyst as calculated bysubtraction of the support's bulk density was 298.2 g/l.

The catalyst had a crush strength of 92.6N.

EXAMPLE 18

The catalyst of Example 17 was used to catalyse an ethylene hydrationreaction.

The hydration reaction was carried out in an 8 litre continuous flowpilot plant, designed to simulate the reaction section of a gas phaseethylene hydration plant. The plant was operated as follows:

Fresh ethylene gas was fed to the plant from a high pressure ethylenecompressor. Liquid water was fed (by diaphragm metering pump) into a“drip-feed” vaporiser, which converted the liquid water into steam. Thefeeds were then combined with recycled ethylene, and passed through thecatalyst bed.

The catalyst was held in a copper lined tubular reactor, which was alsofitted with a central multipoint thermocouple for accurately measuringcatalyst temperatures at various (fixed) depths down the catalyst bed.The gaseous reactor effluent was cooled to ambient temperature using asimple shell and tube type heat exchanger. The mixture of liquid andgaseous products were separated in a high pressure gas/liquid separator.The gaseous product, still containing significant levels of ethanol, wasthen further processed by passing it through a wash tower. In the washtower, the majority of the water soluble components was removed from thegaseous product.

The liquid effluent from-the wash tower was then mixed with the liquideffluent from the gas/liquid separator to form the main product stream.This stream was collected and analysed (by gas chromatography) on aregular basis to provide catalyst activity and selectivity data.

The scrubbed gas from the wash tower was fed to a recycle compressor andreturned to the reactor. The recycle gas flow rate was carefullycontrolled using a Coriolis meter to provide a similar contact timethrough the catalyst bed as that encountered in commercial ethanolplants. An on-line gas chromatograph was also employed to analyse therecycle stream.

The plant was operated at a 1000 psig (68 atm) pressure, a reactor inlettemperature of 240° C., a reactor exit temperature of 265° C.; a[water]:[ethylene] feed mole ratio of 0.28-0.30; a typical ethylene GHSVof 1250 hr⁽⁻¹⁾; and a typical steam GHSV of 357.6 hr⁽⁻¹⁾.

The catalyst was kept on stream for 2 weeks, during which time theethylene STY of the process was measured 20 times, at regular testintervals. The results are shown in FIG. 9 below.

As can be seen from the graph of FIG. 9, the catalyst of Example 17 issignificantly more active than prior art catalysts, such as phosphoricacid supported on Degussa 350 (Comparative Example 13).

In fact, the performance of Example 17 is comparable to that of acatalyst supported on a conventional silica gel, such as Grace 57 interms of spot productivity. However, as shown by the results of Example19 and Comparative Example 20 (below), the catalyst of Example 17 isconsiderably superior to Grace 57 in terms attrition resistance.

After use, the pellet crush strength of the catalyst was found to haveimproved from 92.6N (fresh catalyst) to 169.4N (used catalyst). Thiscompares favourably to the crush strengths of catalysts supported onDegussa 350, which have fresh and used crush strengths of 77N and 148 N,respectively.

The pore size distribution (PSD) of the used catalyst of Example 17 wasalso found to be different to that of the fresh catalyst. After onepilot run, the used support was found to be broad uni-modal at 171 nm.Although the PSD of the support had opened up, this was not to the samedegree as prior art supports such as Degussa 350. After use, Degussa 350supports were found to be bimodal at 200 nm and 3000nm.

EXAMPLE 19

Attrition resistance of the catalyst of Example 17 was quantified bymeasuring the amount of dust/broken pellets (fines) generated before andafter use.

When the fresh catalyst was sieved through a 2 mm sieve, and thecollected fines weighed on an analytical balance, only 0.05% wt fineswere found to have been generated. After a 2 week run, the catalyst wassieved through a 2mm sieve. The collected fines were weighed on ananalytical balance. Only 0.6% wt fines had been generated (some of whichby the act of removing the catalyst from the reactor, and not by theprocess).

COMPARATIVE EXAMPLE 20

In this Example, the attrition resistance of a phosphoric acid catalystsupported on a silica gel (Grace 57) support was measured using theprocess of Example 19.

After a 2 week run, the silica gel catalyst was sieved through a 2mmsieve. The collected fines were weighed on an analytical balance. 10 wt% fines had been generated.

A comparison of the results of Example 19 and Comparative Example 20shows that the catalyst of Example 18 is considerably superior to Grace57 in terms of attrition resistance.

EXAMPLE 21

Since titanium is added to the catalyst support to stabilise thesupport's physical structure, it is important that the titanium is notlost from the support when subjected to process conditions. Hence,samples of the used catalyst of Example 18 were analysed for Ti contentusing X-ray Fluorescence. The results were compared to the Ti content ofthe unused catalyst. It should be noted that the used catalyst wassubjected to Soxhlet extraction prior to analysis in order to remove theorthophosphoric acid catalyst, and any dissolved titanium.

The titanium content of the support has marginally decreased from 4.0 to3.8% wt/wt in the first run. However, the used catalyst has retained ca.3% phosphorus, and the bulk density of the support changes as a result.When this is taken into account, there is no evidence for any Ti lossfrom the support (to within the accuracy of the XRF technique).

In addition, there was no evidence for Ti leaching during catalystpreparation and operation.

EXAMPLE 22

A catalyst support in accordance with this invention was prepared bymixing 1.0 kg of pyrogenic silica (Aerosil® 200 V from Degussa-Huels,amorphous), 60 g of zirconium hydroxide, 20 g of methylcellulose, 50 gof wax, 5 g of polysaccharide, 10 g of a 30% ammonia solution and 1.85kg of water. The mixture was kneaded for approx. 30 minutes and wassubsequently extruded. After drying at 110° C., the material wascalcined in air at 850° C. for 3 hours. The obtained extrudates contain5 wt.-% of ZrO₂ and 95% of SiO₂. wt.-%. The diameter of the extrudatesis 4.0 mm, the pore volume is 0.97 ml/g, the bulk density 460 g/l andthe crush strength 58 N.

This support was loaded with phosphoric acid and heated to 370° C. in ahigh pressure apparatus at a steam pressure of 15 bar for approx. 45hours. The pore size distribution of the aged catalyst was determined byHg porosimetry. The pore size distribution is shown graphically in FIG.10. Substantial part of the pores has a diameter smaller than 5 μm.

Further variations and modifications of the foregoing will be apparentto those skilled in the art and are intended to be encompassed by theclaims appended hereto.

1. A catalyst support comprising synthetic silica, with 0.5-10 parts ofone or more oxides or phosphates of the elements of group IIA, IIIB,IVB, VB, VIB, VIIB, VIII, IB, IIB, IIIA, IVA and the lanthanides,whereby the support is prepared by mixing particulate synthetic silicawith particulate oxides or phosphates of the elements of Groups IIA,IIB, IVB, VB, VIB, VIIB, VIII, IB, IB, IIIA, IVA and the lanthanides, orwith precursors thereof, a shaping and calcining to form a finishedsupport having particulate oxide or phosphate domains.
 2. The catalystsupport according to claim 1, wherein the oxides or phosphates of theelements include titania and/or zirconium dioxide.
 3. The catalyssupport according to claim 1, wherein the content of synthetic silica inthe calcined support is at least 80% by weight based on the total weightof the support. 4-7. (canceled)
 8. The catalyst support according toclaim 1 wherein the synthetic silica comprises pyrogenically producedsilica.
 9. The catalyst support according to claim 1 wherein thesynthetic silica consists entirely of pyrogenically produced silica. 10.(canceled)
 11. The catalyst support according to claim 1 wherein thetitania comprises pyrogenically produced titania.
 12. The catalystsupport according to claim 1 wherein the titania consists entirely ofpyrogenically produced titania.
 13. The catalyst support according toclaim 1 wherein the titania comprises precipitated titania.
 14. Thecatalyst support according to claim 1 wherein the titania consistsentirely of precipitated titania.
 15. The catalyst support according toclaim 1 wherein the zirconium dioxide comprises pyrogenically producedzirconium dioxide.
 16. The catalyst support according to claim 1 whereinthe zirconium dioxide consists entirely of pyrogenically producedzirconium dioxide. 17-18. (canceled)
 19. A process for the preparationof a catalyst support according to claim 1, which comprises mixingparticulate synthetic silica with 0.5 to 10 parts by weight ofparticulate oxides or phosphates of the elements of Groups IIA, IIIB,IVB, VB, VIB, VIIB, VIII, IB, IB, IIIA, IVA and the lanthanides, or withprecursors thereof, based on the total weight of the support, prior tothe forming step, a forming and calcining between 400 and 1050° C.
 20. Aprocess for the preparation of a catalyst support according to claim 2,which comprises: mixing particulate silica, with 0.5 to 10 parts byweight of particulate titania and/or zirconium dioxide or withprecursors thereof, based on the total weight of the support, prior tothe forming step; a forming step and calcining the formed materialbetween 400 and 1050° C.
 21. (canceled)
 22. The catalyst supportaccording to claim 1, wherein the domains are titania and/or zirconiumdioxide.
 23. The catalyst support according to claim 1, wherein thedomains are distributed throughout the support.